Whether it is an Alfa or not depends only upon whether they officially authorized the construction. There is a long history of ultra-low production specials that are rightly considered to be part of the Alfa legacy. Most contained a variety of Alfa components, while the rest was custom-made. Beyond the engine, the original TZs were essentially unrelated to mass produced cars, and the engines were, of course, barely related to road going cars.
If we assume Alfa blessed the use of their name and traditional grille, we might still wish that SOMETHING from the production cars was used. I would have thought the V8 from an 8C would have been fine, although even that was taken from a cousin’s parts bin. I guess it is fair to accept the Viper contributions as being from within the family, although unlikely to warm the hearts of us old guys.